The acute neuralgia produced by recrudescence of latent varicella-zoster virus (familiarly known as chicken pox virus) is called herpes-zoster, or "shingles". Reactivation of the latent virus in a dorsal root ganglion results in the transport of live virus along the associated sensory nerves (dermatome).
In addition to severe pain in the distribution of affected nerves, herpes zoster is also associated with nervous system complications such as myelitis, stroke, ocular damage, skin damage, and, most commonly, post-herpetic neuralgia--defined as pain that persists in the involved dermatome for more than 1 month after healing of the skin lesions.
Over 50% of people over age 60 who have acute herpetic neuralgia can expect to be afflicted with PHN. The disorder resolves spontaneously within 1 year in most cases, but in some the pain persists for life.
Pain management in both herpes zoster and post-herpetic neuralgia is unsatisfactory. Non-steroidal anti-inflammatory medications and opiates are often of little benefit. The only drug with proven effectiveness in a controlled study is the tricyclic antidepressant amitripyline. This drug has multiple effects that are not well tolerated by elderly patients, and pain relief is incomplete.
Other medications--anticonvulsants (eg, carbamazepine) and neuroleptics (eg, chlorprothixene)--are widely used but have not proved to be effective. Several topical preparations, including salicylate poultices, ethyl chloride spray, idoxurine (an anti-viral agent) in DMSO, and others have been anecdotally reported to be effective.
Local anesthetics, such as lidocaine, have been administered parenterally to relieve the pain of herpes zoster and post-herpetic neuralgia: as regional sympathetic blocks, as peripheral nerve blocks, by epidural infusion, by direct subcutaneous infiltration, and intravenously.
However, topical application of local anesthetics is not a presently recognized method of treating pain associated with herpes zoster and post-herpetic neuralgia.